The threshold interpolation conjecture for consecutive patterns in random permutations

Let σn,m\boldsymbol{\sigma}_{n,m} be a uniformly random permutation of [n][n] with exactly mm inversions. For a permutation ρ\rho, write ρ\rho for its complement by replacing each entry ii with ρ+1i|\rho|+1-i, and let σn,m\boldsymbol{\sigma}_{n,m} contain ρ\rho mean that ρ\rho occurs as a consecutive pattern. For a permutation ρ\rho, let inv(ρ)\operatorname{inv}(\rho) denote its number of inversions. Let π\pi be any consecutive permutation pattern, and set

s=inv(π),s=inv(π).s=\operatorname{inv}(\pi),\qquad s'=\operatorname{inv}(\overline{\pi}).

The threshold interpolation conjecture. If n11/smn^{1-1/s}\ll m and (n2)mn11/s\binom{n}{2}-m\gg n^{1-1/s'}, then

limnP[σn,m contains π]=1.\lim_{n\to\infty}\mathbb{P}\big[\boldsymbol{\sigma}_{n,m}\text{ contains }\pi\big]=1.

The preceding theorem establishes the appearance and disappearance thresholds separately, while this conjecture asserts almost-sure presence throughout the interval between them. The paper notes that its random-composition methods do not establish this intermediate regime.

Sources & referencesView supporting material

Primary source

David Bevan and Dan Threlfall, “Thresholds for patterns in random permutations with a given number of inversions”, arXiv:2312.01182 (2024).

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